Do destratification fans cut heating costs?
Updated 23 October 2026 · SEO Dons Editorial
Destratification fans move warm air that has risen under the roof back towards the floor. Whether they pay depends on how much heat is stranded at the top of the building and what that heat costs.
What is stratification, and why does it waste heat?
The Carbon Trust's warehousing guide says stratification is caused by cold air entering a building, displacing the warm air inside towards the roof, with the incoming cold air remaining at floor level. Destratification fans can counteract this by moving the trapped warm air downwards, and the guide says the heating system can then reduce its output.
Height makes the problem bigger. A CIBSE Journal module cites CIBSE Guide A as saying that in a 3 metre office a heated-air system needs up to 5% more heating than radiators, and that the extra loss rises as the space gets taller. The same module notes that the actual temperature gradient depends on the height of the space.
How are destratification fans different from HVLS fans?
Destratification fans recover heat in the heating season. HVLS fans (high-volume, low-speed) are about air movement for people, which matters in summer: HSE says moving air in warm or humid conditions can increase heat loss through convection without any change in air temperature. The HVLS fans guide covers that case.
In winter, air movement at working height can be unwelcome. HSE says small air movements in cool or cold environments may be perceived as a draught as people are particularly sensitive to them, so air speed at working height is worth asking about.
What decides the saving?
- Roof height. On CIBSE's reading the extra heating needed by a heated-air system rises with height, so a taller space has more heat to recover.
- Heating type. Warm-air equipment raises the air temperature in the space. The Energy Technology List (ETL) says radiant heating keeps the air temperature significantly lower than fan convectors or low temperature radiators, which suggests less warm air to pool. Measure before assuming fans will help a radiant system.
- Air tightness. Cold air entering is what drives stratification, and the ETL says typically 35% of the heated air in commercial buildings is lost through ventilation and air infiltration. Fans move heat around; they do not stop it leaking out. The Carbon Trust says insulation and air-tightness should be prioritised, and suggests door interlocks so heating runs only when loading doors are closed; the air curtains guide covers a related fix.
- Controls. Approved Document L says central plant should operate only when the zone systems require it. A sensible specification has the fans following the same logic and running only when heating is on. The ETL's criteria for warm-air controllers include an optimum start mechanism.
What could the fans save? A worked estimate
The Carbon Trust's warehousing checklist lists a saving of about 25% on heating energy against its destratification fan action. That is a general figure from a 2019 guide, not a prediction for any building, so the example below tests lower savings and subtracts the fans' own electricity.
DESNZ's annual report gives average non-domestic prices across all size bands, including the Climate Change Levy: 24.3 pence per kWh for electricity and 5.3 pence for gas in 2025 (provisional). Suppose, for example, a warehouse burns 100,000 kWh of gas a year in warm-air heaters, a bill of £5,300 at those prices. Assume six fans drawing 0.1 kW each for 2,000 hours: 1,200 kWh of electricity, or £292. The fan power and hours are placeholders; a data sheet gives the real figures.
| Cut in gas use | Gas saved | Value at 5.3p | Fan electricity | Net a year |
|---|---|---|---|---|
| 5% | 5,000 kWh | £265 | £292 | −£27 |
| 10% | 10,000 kWh | £530 | £292 | £238 |
| 15% | 15,000 kWh | £795 | £292 | £503 |
| 25% | 25,000 kWh | £1,325 | £292 | £1,033 |
The break-even is about 5.5% of the gas. The reason is the price gap: electricity costs about 4.6 times as much per kWh as gas (24.3 divided by 5.3), so every kWh of fan electricity must displace about 4.6 kWh of gas before it saves anything. On the same assumptions, a building heated by 100,000 kWh of electricity would break even at about 1.2% and save £2,138 net at a 10% cut. Payback is the installed cost divided by the net saving, so ask for the cost in writing.
What should a proposal for destratification fans state?
- The building height and the heating system it sits under: warm air, radiant or wet.
- The number and position of fans, the power of each in kW and the hours they are expected to run.
- The control strategy: what starts and stops the fans, and how that follows the heating.
- The floor-to-roof temperature difference expected before and after, and how it will be measured.
- Air speed at working height, given HSE's point about draughts.
- The basis of any percentage saving, with the test evidence and date behind it.
- The installed cost, so payback can be calculated.
How can the saving be checked?
Approved Document L says energy submetering should be installed when fixed building services are provided or extended in an existing building, so heating fuel can be read separately. Compare use per degree day before and after, as in the degree days guide, and record the floor-to-roof temperature difference. A supplier's headline percentage means little without the building height, heating type, door use and test method behind it. The warehouse heating guide compares the heating systems the fans would sit under, and the commercial heating systems page covers the wider choice. Readers can send an enquiry through the form on this page.
Sources
All pages checked 22 October 2026.
- DESNZ: annual report, performance report (updated 19 August 2026); Energy Technology List and warm-air criteria.
- HSE: thermal comfort. MHCLG: Approved Document L Volume 2 (2021 edition).
- Carbon Trust: warehousing guide (February 2019). CIBSE Journal: boiler module (May 2016).
Common questions
Do destratification fans work in summer?
Their job is to recover heat, which matters in the heating season. In summer, HSE says moving air in warm or humid conditions can increase heat loss through convection without any change in air temperature. That is a comfort effect, and HVLS fans are the usual answer to it.
Is there a minimum roof height for destratification fans?
No official threshold turned up in the sources checked. CIBSE's reading is that the extra heating a heated-air system needs rises with height, so the taller the space the more there is to recover. Ask the supplier what floor-to-roof temperature difference they expect, then measure it.
Do destratification fans save more on electric heating?
Per kWh, yes, because electricity costs more than gas: 24.3 pence against 5.3 pence in DESNZ's 2025 provisional averages. In the worked example a 10% cut on 100,000 kWh of electric heating is worth £2,430 a year against £530 for gas, while the fans' electricity stays at £292.
Can destratification fans cause draughts?
They can if air speed at working height is too high. HSE says small air movements in cool or cold environments may be perceived as a draught, and that people are particularly sensitive to them. Fan position and speed are worth checking at commissioning.
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